Unlike zebrafish (Danio rerio), medaka (Oryzias latipes) have been considered to be incapable of cardiac regeneration. In a new comparative study, Miguel Angel Garitagoitia-Romero, María Galardi-Castilla, Miguel Torres and Nadia Mercader put this assumption to the test by performing a detailed side-by-side analysis of heart regeneration in medaka and zebrafish following cardiac cryoinjury. Their findings reveal that medaka possess a far greater regenerative capacity than previously recognized.

The researchers identified many of the same regenerative processes seen in zebrafish, including cardiomyocyte proliferation, transient blood vessel formation, regression of fibrotic scar tissue, and recovery of cardiac function in a subset of animals. While these responses were generally slower or less complete than in zebrafish, they demonstrate that medaka do not entirely lack a regenerative response as previously believed.

Importantly, the study extended beyond tissue-level measurements to assess how heart injury affects whole-animal performance. Using a Swimming tunnel from Loligo® Systems, the authors measured critical swimming speed (Ucrit) in both species during recovery. Despite a measurable decline in cardiac function after injury, swimming performance was unaffected in either medaka or zebrafish, indicating that the regenerative process preserves overall exercise capacity.

This work provides new insight into the diversity of regenerative responses among teleost fishes and suggests that medaka occupy an intermediate position between highly regenerative and poorly regenerative species. The study establishes medaka as an important comparative model for understanding the cellular and physiological mechanisms that govern heart repair.

The paper titled Comparison of cardiac regeneration capacity between zebrafish and medaka reveals a regenerative response in both teleost species is published in npj Regenerative Medicine and can be found online at https://doi.org/10.1038/s41536-026-00482-x

Do you want to learn more about the Swim Tunnel system used in this paper?

• Swim Tunnel System
• AutoSwim 2: Computerized and automated water velocity control
• More papers published using our Swim Tunnels